Everyone who builds web applications should read the Reckoning series by @slightlyoff https://infrequently.org/series/reckoning/
My own notes here, but you should work through the entire thing: https://simonwillison.net/2024/Aug/18/reckoning/
Seriously, take a look at the case-study in which the California food stamps signup site takes 29.5s to become interactive on a slow rural mobile connection, and tell me we don't urgently need to do better! https://infrequently.org/2024/08/object-lesson/#the-golden-wait
@simon @slightlyoff one of the good things that uk Government Digital Service did was to develop a standard designed (as far as i can tell) for low end devices and connections.